Four years into the criminal investigation of the nation’s worst mining disaster in decades, federal officials told ABC News that prosecutors are now focused on the role of West Virginia coal boss Donald L. Blankenship.

“I believe this permeated from the top down – from Don Blankenship down,” said U.S. Sen. Joe Manchin, D-W.V., who was governor at the time of the blast. “I believe that Don has blood on his hands. And I believe that justice will be done.”

Pressure has been steadily increasing for prosecutors to make their move against the controversial former chief executive of Massey Energy, which owned and operated the Upper Big Branch mine when 29 coal workers were killed in an explosion in April 2010.

Federal officials have prosecuted four Massey employees -- most recently exacting a guilty plea from a high ranking official who acknowledged that the company employed a practice of tipping off mine workers when a safety inspector was coming onto the site.

U.S. Attorney R. Booth Goodwin II told ABC News that prosecutions to date show his office has been methodically going “up the line, and consistently so” in assessing whether conduct by mine operators may have led to the explosion.

“What we have seen is a conspiracy to violate mine safety and health laws,” Goodwin said. “And that conspiracy was very pervasive.”

Official state and federal investigations into the tragedy have already concluded that loss of life could have been avoided had the mine been operated more safely.

Families of the victims, angered by the slow pace of the criminal probe, held a rally in front of the federal court house Wednesday demanding justice in the case.

Meanwhile, Blankenship has launched a preemptive public relations onslaught, releasing a 50-minute film called “Never Again” which offers what he says is proof that the explosion was the result of an unexpected surge of natural gas into the mine shaft – not the result of safety deficiencies.

In an hour-long interview with ABC News, portions of which will be broadcast tonight on “World News With Diane Sawyer” and “Nightline,” Blankenship argued that scientific evidence will vindicate him.

“No one ever did more for improving or trying to improve safety,” Blankenship said.

In the film, and in interviews he is giving this week, Blankenship speaks at length about his views on the mining disaster, focusing attention on what he believes are shortcomings by federal regulators who could be doing more to make mines more safe.

The public relations offensive comes after Blankenship refused to participate in the official state and federal investigations into the disaster – with his lawyer invoking his fifth amendment rights in a letter to investigators. Blankenship told ABC News he declined to meet with investigators because he did not believe they would treat him fairly.

“Because the people doing the investigating were also doing the regulating and the inspecting,” he said. “And when you’re investigating yourself, it’s not going to be a fair investigation.”

Blankenship has long been a larger-than-life figure in West Virginia, where he was once accused of making campaign donations to try and tilt the balance of the state supreme court in his favor, and where his strong-fisted leadership of the giant coal conglomerate made him both famous and feared.

Asked directly about the criticism he has faced for the way he managed his company, Blankenship said he was unmoved by it.

“I would prefer to be liked by everybody,” he said. “And I think I've done things that should warrant that. But I can't affect the way people think. Everybody has their own opinions.”

Blankenship’s financing of a documentary about the Upper Big Branch disaster has touched a sensitive nerve in his home state.

Manchin, who appears in the documentary, said he was tricked into appearing in the film, and is outraged by what he called a “callous” attempt by Blankenship to rewrite history.

“Don is taking his millions of dollars that he made off the sweat and blood of the miners and using it now, trying to turn things around and vindicate himself,” Manchin said. “Now you talk about a cynical approach to something. That’s heartless. And that’s about as bad as it gets.”

The investigations specifically cited safety violations at the Massey-owned mines as having contributed to the deadly outcome. Davitt McAteer, a West Virginia mining expert, helped lead one of the official investigations into the disaster. The report he helped author includes a section about the culture Blankenship fostered at mines owned by Massey – a culture where McAteer said coal production goals were paramount.

“That is exactly what we call the Massey way. A disregard of fundamental basic principles,” he told ABC News in an interview. “These are not new protections. These protections have been around for 100 years. We’ve known we need to keep ignition source away from methane, we've known we need to keep away coal rock dusted; we've known we have to ventilate to push that methane out. The failure to do that - mines have a danger in them.”

Blankenship said he believes at least some of those who lost loved ones in the mine disaster will appreciate his efforts to promote safer conditions through his film.

“I know that if I had lost a loved one, that improvements being made in safety in his honor, and having a documentary that gives me at least a perspective of what actually happened – that I would appreciate it,” he said.

But that’s not what 10 relatives of the victims told ABC News after viewing the video. Those relatives said they continue to harbor strong feelings about Blankenship and his film, and they are not positive or appreciative.

“It was just like a slap to our faces that he would do this on the anniversary of this,” said Sherry Mullins Scurlock, whose brother Rex died in the blast.

“He’s just making us stand together harder and firmer, and we’re going to fight longer and harder,” said Clay Mullins. “He might have more money, but he ain’t got more fight.”